A silent chain may be used as a power transmission chain or a timing chain for an automobile or a motorcycle. As illustrated in FIGS. 5 and 6, for example, a silent chain 1′ may have a configuration in which many link plates 2′ each having a pair of tooth parts 21′ and pin holes 22′ are stacked in the thickness direction as well as in the length direction, and respective link plates 2′ are linked together using linking pins 3′ inserted into respective pin holes 22′. Guide links 4′ can be provided on the outermost sides of link plates 2′, and the ends of linking pins 3′ can be fixed in pin holes 41′ of guide links 4′. Furthermore, here, a case is exemplified in which a so-called low rigidity guide link, which has a crotch part created on its rear side, can be utilized for the guide link.
In this kind of silent chain, as illustrated in FIG. 7a, the link hole diameter of link plate 2′ can be denoted as φDl′, and the pin diameter of linking pin 3′ as φd, establishing a relationship that may be expressed as φDl′>φd. In addition, as illustrated in FIG. 7b, the pin hole diameter of guide link 4′ can be denoted as φDg′, establishing a relationship that can be expressed as φDg′<φd.
In other words, link plate 2′ and linking pin 3′ may be fitted with a clearance, whereby respective link plates 2′ can rotate around linking pins 3′ in order to allow the entire chain to bend. Conversely, guide link 4′ and linking pin 3′ may be fitted tightly, and respective guide links 4′ are press-fit to linking pins 3′, whereby, linking pins 3′ can be prevented from falling out.
In addition, the distance from pin hole centerline Ll′ of link plate 2′ to rear surface or chain guide contact surface 23′ can be denoted as hl′, and the distance from pin hole centerline Lg′ of guide link 4′ to rear surface or chain guide contact surface 43′ of guide link 4′ can be denoted as hg′, establishing a relationship that may be expressed as hl′=hg′.
As illustrated in FIG. 8, when the silent chain with such a configuration is driven, wear 52 may result due to abrasion of guiding surface 51 of chain guide 5.
The following mechanism may be considered to account for this wear. When a conventional silent chain makes contact with the chain guide, clearance c (=φDl′−φd) may be created between pin holes 22′ of respective link plates 2′ and linking pins 3′, as illustrated in FIG. 9. Accordingly, clearance e′ (=c/2) may be created between guiding surface 51 of chain guide 5 and the rear surface 23′ of respective link plates 2′.
When a conventional silent chain runs on guiding surface 51 of chain guide 5 under such conditions, if only guide links 4′ make contact with guiding surface 51, the pressure of the contact surface against the guiding surface 51 may increase. As a result, edge-like abrasive wear 52 may be created on guiding surface 51 after the chain is driven for some time, if only guide links 4′ make contact with the guiding surface 51.
Another configuration of a silent chain may comprise a rear wheel-driving silent chain, such as used as power transmission chains or timing drive chains for automobiles and motorcycles, is illustrated in FIGS. 12 and 13, where like reference numerals with the above-described conventional silent chain generally indicate similar elements in the conventional rear wheel-driving silent chain. For example, rear wheel-driving silent chain 1′ may comprise a plurality of link plates 2′, each having a pair of pinholes 21′ and a pair of teeth 22′ on either side of the center line of the pinholes, stacked in the thickness direction as well as in the length direction. Respective link plates 2′ may be linked together using linking pins 3′ inserted into respective pinholes 21′. Guide links 4′ can be provided on the outermost sides of link plates 2′, and ends of linking pins 3′ can be fixed in pinholes 41′ of guide links 4′.
In this kind of rear wheel-driving silent chain, as illustrated in FIG. 14a, the link hole diameter of link plate 2′ can be denoted as φDl′, and the pin diameter of linking pin 3′ can be denoted as φd, establishing a relationship which may be expressed as φDl′>φd. In addition, as illustrated in FIG. 14b, the pin diameter of guide link 4′ can denoted as φDg′, establishing a relationship which may be expressed as φDg′<φd.
In other words, link plate 2′ and linking pin 3′ are formed with a clearance; whereby, respective link plates 2′ rotate around linking pins 3′ in order to allow the entire chain to bend. In contrast, guide link 4′ and linking pin 3′ may be fit together tightly, and respective guide links 4′ may be press-fit to linking pins 3′; whereby, linking pins 3′ can be prevented from falling out.
In addition, the distance from pinhole center line Ll′ of link plate 2′ to chain guide contact face 23′ is denoted as hl′, and the distance from pinhole center line Lg′ of guide link 4′ to chain guide contact face 43′ of guide link 4′ can be denoted as hg′, establishing a relationship which may be expressed as hl′=hg′. Furthermore, in this case, chain guide contact faces 23′ and 43′ are provided respectively on either side of pinhole center lines Ll′ and Lg′ of link plate 2′ and guide link 4′.
As illustrated in FIG. 15, when this kind of conventional rear wheel-driving silent chain contacts the chain guide, clearance c (=φDl′−φd) is created between pinholes 21′ of respective link plates 2′ and linking pins 3′. Accordingly, clearance e′ (=c/2) is created between guiding face 51 of chain guide 5 and chain guide contact face 23′ of respective link plates 2′.
It is conceivable to eliminate such clearance e′ in order for chain guide contact face 23′ of link plate 2′ to contact guiding face 51 of chain guide 5. However, chain guide contact face 23′ is provided at the tip of triangular tooth 22′, so that the area in contact with guiding face 51 is small. Thus, when chain guide contact face 23′ contacts guiding face 51, the contact face pressure on chain guide contact face 23′ increases, and abrasion of chain guide contact face 23′ and guiding face 51 can be assumed to take place. In contrast, chain guide contact face 43′ of guide link 4′ is a flat surface, so that the area in contact with guiding face 51 is large.